Method and apparatus for controlling gain level of a supplemental channel in a CDMA communication system

ABSTRACT

In a code division multiple access communication system ( 100 ), a method and accompanying apparatus provide for controlling gain of a forward supplemental channel ( 482 ) by determining gain level of a forward fundamental channel ( 481 ) associated with supplemental channel ( 482 ) for being targeted for a common mobile station, determining an adaptive margin (Ma) for fundamental channel ( 481 ) and determining a forward supplemental channel gain (Gsch) based on the gain of supplemental channel ( 482 ) and the Ma. The Gsch may be successively decreased for subsequent data frames targeted for the common mobile station on supplemental channel ( 482 ) by successively decreasing the Ma until receiving a supplemental channel frame erasure indicator from the common mobile station. The Gsch may be increased for a subsequent data frame targeted for the common mobile station on supplemental channel ( 482 ) by increasing the Ma after receiving the supplemental channel frame erasure indicator from the common mobile station.

CLAIM OF PRIORITY UNDER 35 U.S.C. §120

The present Application for Patent is a Continuation and claims priorityto patent application Ser. No. 09/895,375 now U.S. Pat. No. 6,937,584entitled “Method and Apparatus for Controlling Gain Level of aSupplemental Channel in a CDMA Communication System” filed Jun. 29,2001, now allowed, and assigned to the assignee hereof and herebyexpressly incorporated by reference herein.

BACKGROUND

1. Field

The present invention relates generally to the field of communications,and more specifically, to communications in a cellular communicationsystem.

2. Background

In code division multiple access (CDMA) communication systems, a numberof users in the same geographical area may choose to operate on a commoncarrier frequency. The signal from each user is encoded according to aunique assigned code. A receiver may receive signals from differentusers with a common carrier frequency. While a signal for one user isbeing decoded, the signals transmitted from all other users may betreated as interference. A receiver decodes each signal according to theassigned code. Moreover, excessive transmission by a user may causeinterference for other users in addition to causing system overload at abase station. In a CDMA system, the power level of the signalstransmitted by different users of the system is controlled to controlthe interference level. The power level of each signal is controlled atthe transmitter to maintain an adequate quality of reception at areceiving end. Other reasons, such as conserving battery power, forcontrolling power level of signals in a CDMA system are well known byone of ordinary skill in the relevant art.

Although the power level of the transmitted signal from each user iscontrolled to maximize the use of the available channels, there is aneed for an increased mobility and higher quality of communicationservices. Such communication services may include wireless radiotransmission of digitized speech, still or moving images, text messagesand other types of data. The communication channel between a mobilestation and a base station may be over two or more related communicationchannels. One of the channels may be a fundamental channel, and anothermay be a supplemental channel. The fundamental channel may serve as theprimary channel for all the traffic communications between thetransmitter and the receiver. The supplemental channel may carryadditional data. The supplemental channel may be bursty. The gain levelof each channel may be based on the received quality level at thereceiver. However, the bursty nature of the supplemental channel maycreate an inefficient power control scheme in the communication system.The power level may be based on the gain level of each communicationchannel through a power control scheme in the communication system.

To this end as well as others, there is a need for an efficient gaincontrol of the supplemental channel in a communication system.

SUMMARY

In a code division multiple access communication system, a method and anaccompanying apparatus provide for controlling gain of a forwardsupplemental channel by determining gain level of an associated forwardfundamental channel (Gfch), determining an adaptive margin (Ma) for theforward supplemental channel and determining a forward supplementalchannel gain (Gsch) based on the Gfch and the Ma. The forwardsupplemental channel is transmitted to the mobile station at thedetermined Gsch level. A data rate factor based on a data rate of theforward fundamental channel and a data rate of the forward supplementalchannel may be determined. The Gsch may be based additionally on thedata rate factor. The Gsch may be successively decreased for subsequentdata frames targeted for the common mobile station on the forwardsupplemental channel by successively decreasing the Ma. The Gsch may beincreased for a subsequent data frame targeted for the same commonmobile station on the forward supplemental channel by increasing the Maafter receiving a supplemental channel frame erasure indicator from thecommon mobile station.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, objects, and advantages of the present invention willbecome more apparent from the detailed description set forth below whentaken in conjunction with the drawings in which like referencecharacters identify correspondingly throughout and wherein:

FIG. 1 illustrates a communication system 100 capable of operating inaccordance with various embodiments of the invention;

FIG. 2 illustrates a communication system receiver, for operation in amobile station and a base station, capable of operating in accordancewith various embodiments of the invention;

FIG. 3 illustrates a flow chart for controlling power level of acommunication channel between a mobile station and a base station,capable of having adjusted operating parameters in accordance withvarious embodiments of the invention;

FIG. 4 illustrates an exemplary forward link channel structure;

FIG. 5 illustrates an exemplary reverse link channel structure;

FIG. 6 illustrates an exemplary power control channel frame structure;

FIG. 7 illustrates various exemplary modes of forward link powercontrol;

FIG. 8 illustrates a communication system transmitter capable ofoperating in accordance with various aspects of the invention;

FIG. 9 illustrates an exemplary channel fading condition and associatedchannel gain conditions;

FIG. 10 illustrates an exemplary supplemental channel gain leveldetermined in accordance with various aspects of the invention; and

FIG. 11 illustrates a flow chart for determining an adaptive margin Maused for determining gain level of a supplemental channel.

DETAILED DESCRIPTION

Various aspects of the invention may be incorporated in a system forwireless communications in accordance with the code division multipleaccess (CDMA) technique which has been disclosed and described invarious standards published by the Telecommunication IndustryAssociation (TIA). Such standards include the TIA/EIA-95 standard,TIA/EIA-IS-2000 standard, IMT-2000 standard, and WCDMA standard, allincorporated by reference herein. A copy of the standards may beobtained by accessing the world wide web at the address:http://www.cdg.org, or by writing to TIA, Standards and TechnologyDepartment, 2500 Wilson Boulevard, Arlington, Va. 22201, United Statesof America. The specification generally identified as WCDMAspecification, incorporated by reference herein, may be obtained bycontacting 3GPP Support Office, 650 Route des Lucioles-Sophia Antipolis,Valbonne-France. The “3^(rd) Generation Partnership Project” (3GPP) isembodied in a set of documents including Document No. 3G TS 25.211, 3GTS 25.212, 3G TS 25.213 and 3G TS 25.214, known as the WCDMA standard.The “TIA/EIA/IS-95 Remote Station-base station Compatibility Standardfor Dual-Mode Wideband Spread Spectrum Cellular System” is known as theIS-95 standard. The “TR-45.5 Physical Layer Standard for cdma2000 SpreadSpectrum Systems” is known as the CDMA-2000 standard. A system forcommunication of data is detailed in the “TIA/EIA/IS-856 cdma2000 HighRate Packet Data Air Interface Specification,” incorporated by referenceherein, is also capable of incorporating various embodiments of theinvention.

Generally stated, a novel and improved method and an accompanyingapparatus provide for an efficient gain control of a supplementalchannel in a CDMA communication system. One or more exemplaryembodiments described herein are set forth in the context of a digitalwireless data communication system. While use within this context isadvantageous, different embodiments of the invention may be incorporatedin different environments or configurations. In general, the varioussystems described herein may be formed using software-controlledprocessors, integrated circuits, or discrete logic. The data,instructions, commands, information, signals, symbols, and chips thatmay be referenced throughout the application are advantageouslyrepresented by voltages, currents, electromagnetic waves, magneticfields or particles, optical fields or particles, or a combinationthereof. In addition, the blocks shown in each block diagram mayrepresent hardware or method steps.

FIG. 1 illustrates a general block diagram of a communication system 100capable of operating in accordance with any of the code divisionmultiple access (CDMA) communication system standards whileincorporating various aspects of the invention. Generally, communicationsystem 100 includes a base station 101 that provides communication linksbetween a number of mobile stations, such as mobile stations 102-104,and between the mobile stations 102-104 and a wireline network 105. Basestation 101 may include a number of components, such as a mobile stationcontroller, a base station controller and a radio frequency transceiver.For simplicity, such components are not shown. Base station 101 may alsobe in communication with other base stations (not shown.) Base station101 communicates with each mobile station 102-104 via a forward link.The forward link may be maintained by a forward link signal transmittedfrom base station 101. The forward link signals targeted for mobilestations 102-104 may be summed to form a forward link signal 106. Eachof the mobile stations 102-104 receiving forward link signal 106 decodesthe forward link signal 106 to extract the information that is targetedfor its user.

Mobile stations 102-104 communicate with base station 101 viacorresponding reverse links. Each reverse link is maintained by areverse link signal, such as reverse link signals 107-109 forrespectively mobile stations 102-104. Base station 101 may also transmita predefined series of data bits on a pilot channel via the forward linkto all mobile stations to assist each mobile station in decoding theforward link signal 106. Each of the mobile stations 102-104 maytransmit a pilot channel to base station 101. The pilot channeltransmitted from a mobile station may be used for decoding theinformation carried by the reverse link signal transmitted from the samemobile station. The use and operation of a pilot channel are well known.A transmitter and a receiver for communicating via the forward andreverse links are included in each mobile station 102-104 and basestation 101.

FIG. 2 illustrates a block diagram of a receiver 200 used for processingCDMA signals. Receiver 200 demodulates the received signal to extractthe information carried by the received signal. Receive (Rx) samples maybe stored in RAM 204. Receive samples are generated by a radiofrequency/intermediate frequency (RF/IF) system 290 and an antennasystem 292. Antenna system 292 receives an RF signal and passes the RFsignal to RF/IF system 290. RF/IF system 290 may be any conventionalRF/IF receiver. The received RF signals are filtered, down-converted anddigitized to form RX samples at baseband frequencies. The samples aresupplied to a demultiplexer (demux) 202. The output of demux 202 issupplied to a searcher unit 206 and finger elements 208. A control unit210 is coupled thereto. A combiner 212 couples a decoder 214 to fingerelements 208. Control unit 210 may be a microprocessor controlled bysoftware and may be located on the same integrated circuit or on aseparate integrated circuit. Decoder 214 may include an equalizer (notshown). The decoding function may be combined with the function of theequalizer in decoder 214. The decoding function in decoder 214 may be inaccordance with soft-output Viterbi algorithm concatenated, with orwithout feedback, with functions of an equalizer.

During operation, receive samples are supplied to demux 202. Demux 202supplies the samples to searcher unit 206 and finger elements 208.Control unit 210 configures finger elements 208 to perform demodulationof the received signal at different time offsets based on search resultsfrom searcher unit 206. The results of the demodulation are combined andpassed to decoder 214. Decoder 214 decodes the data and outputs thedecoded data.

In general for searching, searcher 206 may use non-coherent demodulationof a pilot channel to test timing hypotheses and phase offsetscorresponding to various transmitting sources and multi-paths. Thedemodulation performed by finger elements 208 may be performed viacoherent demodulation of other channels such as control and trafficchannels. The information extracted by searcher 206 by demodulating apilot channel may be used in finger elements 208 for demodulation ofother channels. The searcher 206 and finger elements 208 may provideboth pilot channel searching and demodulation of control and trafficchannels. The demodulation and searching can be performed at varioustime offsets. The results of the demodulation may be combined incombiner 212 before decoding the data transmitted on each channel.Despreading of the channels is performed by multiplying the receivedsamples with the complex conjugate of the PN sequence and assigned Walshfunction at a single timing hypothesis and digitally filtering theresulting samples, often with an integrate and dump accumulator circuit(not shown). Such a technique is commonly known in the art. Receiver 200may be used in base station 101 and mobile stations 102-104 for decodingthe information on respectively reverse and forward links signals. Basestation 101 may employ several of receivers 200 to decode theinformation transmitted from several mobile stations at the same time.

Receiver 200 may also perform interference cancellation through acorrelation process. The received samples, after being read from RAM204, are passed through a correlation process for each received signal.The correlation process may collectively be described as the operationsof searcher 206, finger element 208 and combiner 212. Since the receivedsamples contain samples from the signals transmitted from more than onetransmitting source, the correlation process may be repeated for eachreceived signal. The correlation process for each received signal may beunique because each signal may require a different correlationparameters as of those found in operations of searcher 206, fingerelement 208 and combiner 212. Each signal may include a traffic channeland a pilot channel. The PN sequence assigned to the traffic channel andpilot channel carried by each signal may be different. The correlationprocess may include channel estimation, which includes estimating thechannel fading characteristics based on the result of correlating withthe pilot channel. The channel estimation information is used forcorrelating with the traffic channel. Each traffic channel is thendecoded. The decoding operation of a traffic channel may be combinedwith the operation of an equalizer.

The result from each correlation process may pass through a decodingprocess in decoder 214. If the transmitted channel is encoded via aconvolutional encoding process, the decoding process in decoder 214 isperformed according to the utilized convolutional code. If thetransmitted channel is encoded via a turbo encoding process, thedecoding process in decoder 214 is performed according to the utilizedturbo code.

Each signal may be decoded to provide enough information about whether apass indicator is produced for each cyclic redundancy check (CRC)associated with each transmitted frame of data. Operation and use of CRCin a communication system are well known. If the CRC is passed, thedecoded result of the channel associated with the passed CRC may bepassed on for further receiving operation.

The signals received by base station 101 may be input to receiver 200.Antenna system 292 and RF/IF system 290 receive the signals from themobile stations 102-104 to produce the samples of the received signals.The received samples may be stored in RAM 204. Receiver 200 mayincorporate a number of searchers 206, a number of finger elements 208,a number of combiner 212 and a number of decoder 214 for simultaneouslyperforming the correlation process and the decoding process for all thesignals received from different mobile stations. However, only oneantenna system 292 and RF/IF system 290 may be necessary.

Each time a correlation process is started, searcher 206 and fingerelement 208 may start anew for determining non-coherent demodulation ofa pilot channel to test timing hypotheses and phase offsets. Searcher206, or finger element 208, or searcher 206 and finger element 208 incombination, may determine the signal to interference ratio (S/I) foreach received signal. The ratio Eb/I may be synonymous with the ratioS/I. The ratio Eb/I is a measure of signal energy over interference perunit of a data symbol or data bit. Therefore, S/I and Eb/I may beinterchangeable in some respects. The interference may typically bedefined as the power spectral density of interference and the thermalnoise.

To control interference and maintain an adequate system capacity whileallowing adequate reception at a receiving end, the system controls thegain level of each transmitted channel from each transmitting source, orthe data rate of each transmitted channel or both. The gain level may bedetermined through a power control scheme in the communication system100. Various power control schemes for controlling power levels ofsignals in communication system 100 are known. One or more examples aredescribed in the mobile station-base station Compatibility Standard forWideband Spread Spectrum Cellular Systems, otherwise known as TIA/EIA-95and TIA/EIA-2000 standards, incorporated by reference herein.

The gain level of each channel may be controlled by two independentpower control loops, namely an open loop and a closed loop. The openloop power control is based on the need of each mobile station tomaintain an adequate communication link with the base station.Therefore, the mobile station closer to the base station needs lesspower than the mobile station further away. In the open loop powercontrol, the transmitter sets the gain level of the transmitted channelbased on independent measurements of S/I of at least one receivedchannel, such as pilot, paging, sync and traffic channels.

FIG. 3 illustrates various steps of a flow diagram 300 of an exemplaryclosed loop power control. Operation of closed loop power control method300 begins once a mobile station in communication system 100 seizes aforward link traffic channel. After the initial access attempt by themobile station, the mobile station sets an initial reverse channel gainlevel. The initial gain level setting on the reverse link is thenadjusted during subsequent communications. The closed loop power control300 provide the correction to the open loop power control.

To control the gain level of a reverse link channel from a mobilestation, base station 101 at step 301 measures the signal tointerference ratio (S/I) of the reverse link channel transmitted fromthe mobile station. The measured S/I is compared with a set point S/I atstep 302. The measured S/I may be in the form of Eb/I which is a ratioof bit energy over interference. The set point may be in the same form.The set point is selected for the mobile station. The set point may beinitially based on the open loop power setting by the mobile station.

If the measured S/I is higher than the set point, at step 303, basestation 101 orders the mobile station to lower the gain level of thereverse link channel by an amount, for example 1 dB. When the measuredS/I is higher than the set point, it indicates that the mobile stationis transmitting on the reverse link channel at again level higher thanis needed to maintain an adequate reverse link communication. As aresult, the mobile station is ordered to lower the gain level of itsreverse link channel to reduce the overall system interference. If themeasured S/I is lower than the set point, at step 304, base station 101orders the mobile station to increase the gain level of the reverse linkchannel by an amount, for example 1 dB. When the measured S/I is lowerthan the set point, it indicates that the mobile station is transmittingon the reverse link channel at a gain level lower than is needed tomaintain an adequate reverse link communication. As a result ofincreasing the gain level, the mobile station may be able to overcomethe interference level and provide an adequate reverse linkcommunication.

The operations performed at steps 302-304 may be referred to as theinner loop power control. The inner-loop power control keeps the reverselink S/I at the base station 101 as close as possible to its targetthreshold as provided by the set point. The target S/I is based on theset point selected for the mobile station. The power up or power downmay be performed several times during a time frame. One time frame maybe divided into 16 power control groups. Each power control groupconsists of several data symbols. The power up or power down command maybe transmitted 16 times per frame. If one frame of data has not beenreceived at step 305, the power control loop 300 continues to measureS/I of the reverse link channel during the next power control group atstep 301. The process is repeated at steps 302-304 until at least oneframe of data is received from the mobile station.

A single set point or target may not be satisfactory for all conditions.Therefore, the set point used at step 302 may also change depending on adesired reverse link channel error rate. If one frame of data has beenreceived at step 305, a new S/I set point may be calculated at step 306.The new set point becomes the new S/I target for the mobile station. Thenew set point may be based on a number of factors including the frameerror rate. For example, if the frame error rate is above apredetermined level, indicating unacceptable frame error rate, the setpoint may be raised to a higher level. By raising the set point to ahigher level, the mobile station consequently increases the reverse linkchannel gain level via the comparison at step 302 and a power up commandat step 304. If the frame error rate is below a predetermined levelindicating an acceptable frame error rate, the set point may be loweredto a lower level. By lowering the set point to a lower level, the mobilestation consequently decreases the reverse link channel gain level viathe comparison at step 302 and a power down command at step 303. Theoperations performed at steps 305-306, looping back from step 306 tostep 302 to indicate a new set point and looping back to step 301 formeasuring the S/I of the new frames may be viewed as the outer loopoperation. The outer-loop power control may command once every frame.The closed loop power control may command once every power controlgroup. One frame and one power control group may be, respectively, 20and 1.25 mSec long.

The communication system 100 may employ a forward link power controlscheme to reduce interference. The mobile stations 102-104 communicateto base station 101 periodically about the voice and data quality. Theframe error rate and quality measurements are reported to base station101 via a power measurement report message. The message contains thenumber of frames received in error on the forward link channel during aninterval. The gain level of the forward link channel is adjusted basedon the number of frame errors. For fast response, a reverse link erasurebit may be used to inform base station 101 whether the previous framewas received with or without error. The channel power gain may becontinuously adjusted while monitoring the message or the erasure bit.

Referring to FIG. 4, a forward link channel structure 400 depicts thestructure of code channels that may be transmitted by base station 101.Forward link channel structure 400 includes a forward channel 410.Forward channel 410 may include a forward traffic channel 480 and aforward pilot channel 440. Forward traffic channel 480 includes at leasta forward fundamental channel 481. Each forward fundamental channel 481may have an associated forward supplemental channel 482. The resourcesused for transmission of forward supplemental channel 482 may be sharedamong mobile stations 102-104. As such, forward supplemental channels482 may be referred to as the forward shared supplemental channel 482.The gain levels of forward fundamental channel 481 and the associatedsupplemental channel 482 may be controlled in accordance with variousembodiments.

Referring to FIG. 5, a reverse link channel structure 500 depicts thestructure of reverse link code channels that may be transmitted bymobile stations 102-104. Reverse link channel structure 500 includes areverse link channel 510. Reverse link channel 510, among severalchannels, includes a reverse traffic channel 540 for radioconfigurations three through six. Various radio configurations have beendescribed in the relevant standards incorporated by reference herein.Generally, the communications between base station 101 and mobilestations 102-104 may be limited to a set of predefined data rates andmodulation schemes in each radio configuration. Reverse traffic channel540, among several channels, includes a reverse pilot channel 541, areverse fundamental channel 542 and a reverse power control sub-channel543. The reverse pilot channel 541 and reverse power control sub-channel543 are multiplexed together in each power control group in a frame ofdata. The data communicated via reverse power control sub-channel 543may be used to control gain levels of forward fundamental channel 481and the associated supplemental channel 482 in accordance with variousembodiments.

Referring to FIG. 6, a frame of data 600 depicts multiplexing of thepilot data of reverse pilot channel 541 and power control data ofreverse power control sub-channel 543. Each frame may contain 16 powercontrol groups. A power control group 610 depicts multiplexing of thepilot data of reverse pilot channel 541 and power control data ofreverse power control sub-channel 543 in each power control group. Eachpower control group 610 is used to transmit data of reverse pilotchannel 541 and reverse power control sub-channel 543. The reverse powercontrol sub-channel 543 applies to radio configurations three throughsix. Each mobile station supports the inner and outer power controlloops for the forward traffic channel 480. The outer power control loopestimates the set-point value based on Eb/Nt to achieve the target frameerror rate on each assigned forward traffic channel 480. The inner powercontrol loop compares the Eb/Nt of the received forward traffic channelwith the corresponding outer power control loop set-point to determinethe value of the power control bits to be sent to base station 101 onreverse power control sub-channel 543. The reverse power controlsub-channel 543 may be used by each mobile station 102-104 to transmitto base station 101 an erasure indicator bit (EIB) or a qualityindicator bit (QIB). The value of EIB or QIB from a particular mobilestation determines for base station 101 whether to increase or decreasethe power level on forward traffic channel 480 targeted for thatparticular mobile station, or re-transmission of the data on asubsequent data frame or both.

The communication system 100 may employ several modes of a forward powercontrol scheme. The forward traffic channel 480 includes forwardfundamental channel 481 and forward supplemental channel 482. Theforward fundamental channel 481, for the forward power control, may beconsidered as the primary channel and the supplemental channel 482 asthe secondary channel. One frame of data may be for 20 mSec. Each frameof data may include 16 power control groups. Therefore, if the sixteenpower control groups are used for controlling gain level of a forwardchannel, the feedback rate is at 800 bps. If the gain levels of twoforward channels, such as forward fundamental channel 481 and forwardsupplemental channel 482, are being controlled, the feedback rate isless than 800 bps. To control gain level of the primary and thesecondary channels at different feedback rates, different modes of theforward power control may be used.

Referring to FIG. 7, a table 700 provides various forward power controlmodes in accordance with various embodiments. For example, for the mode“000”, all sixteen power control groups are used for power control ofthe primary channel, such as fundamental channel 481. In anotherexample, in mode “110”, the even numbered power control groups are usedto communicate power control bits relating to the primary channel, suchas fundamental channel 481. The odd numbered power control groups areused to communicate QIB or EIB associated with a secondary channel, suchas the supplemental channel 482. A forward fundamental channel 481 frombase station 101 to a mobile station may have one or two associatedforward supplemental channels, such as forward supplemental channel 482.The associated forward supplemental channel 482 is used to communicatedata to the mobile station in addition to the data being communicated onforward fundamental channel 481. The resources used for communicationsof the supplemental channel 482 may be shared among several forwardfundamental channels.

Referring to FIG. 8, a block diagram of a transmitter 800 is shown inaccordance with various embodiments. Transmitter 800 may be used in basestation 101 for transmitting data to mobile stations 102-104 on forwardfundamental channel 481 and forward supplemental channel 482. An input810 receives data for transmission on forward fundamental channel 481.The data may be received from wire-line network 105. The data may betargeted for a mobile station, such as mobile stations 102-104. Eachmobile station in a forward link communication with base station 101 mayhave a forward fundamental channel 481. Additional data may betransmitted to the target mobile station on forward supplemental channel482.

The data transmitted on forward fundamental channel 481 may be continuosover several data frames 899. Each data frame may be 20 mSec long inaccordance with an embodiment. Data on the forward supplemental channel482 may be transmitted sporadically on several data frames 898 to atarget mobile station. Inputs 850A-850M receive data for transmission onforward supplemental channel 482 for several mobile stations. Asupplemental channel scheduler 860 selects data at input 850 fortransmission in data frames 898 on the supplemental channel 482. In oneexample, supplemental channel scheduler 860 may select from data frames898 the data frames “n, n+3, n+4 and n+8” for transmission of data onthe supplemental channel 482 to mobile station 102. The data frames “n+1and n+7” may be selected for transmission of data on supplementalchannel 482 to mobile station 103. The data frames “n+2, n+5 and n+6”may be selected for transmission of data on supplemental channel 482 tomobile station 104.

On the reverse power control sub-channel 543, the mobile stations102-104 transmit an erasure indicator to the base station 101 duringeach data frame. The erasure indicator indicates erroneous or error-freereceived data on the forward supplemental channel 482. The mobilestations 102-104 do not have prior information about the scheduling ofdata on different data frames 898. The mobile stations 102-104 attemptto decode data on the supplemental channel 482 during every data frame.If the data received on the supplemental channel 482 is received inerror or targeted for another mobile station, an erasure indicatorindicating erroneous reception is transmitted to the base station 101 onreverse power control sub-channel 543. Base station 101 may ignore theerasure indicators from the mobile stations that are not selected fortransmission on the supplemental channel 482. For example, base station101 expects to receive, during data frame “n” with appropriate roundtrip delay time, an erasure indicator indicating erroneous or error-freereception of the transmitted data on the reverse power controlsub-channel 543 from mobile station 102 in response to transmitting thedata on supplemental channel 482 during data frame “n.”

The data on the supplemental channel 482 and fundamental channel 481 aremodulated and encoded in blocks 861 and 862 respectively fortransmission to a mobile station. The modulation scheme and the encodingsteps are described in the specification of at least one of thestandards, such as IS-2000 standard, incorporated by reference herein.

The gain of supplemental channel 482 and gain of fundamental channel 481may be selected by a channel gain selector 890 in accordance with anembodiment. For example, the gain of forward fundamental channel 481 maybe selected based on the forward link power control scheme used in thecommunication system 100. In case, the reverse power control sub-channel543 indicates poor reception of the fundamental channel 481, the gain ofthe fundamental channel 481 may be increased via the forward link powercontrol loops to improve the Eb/Nt at the target mobile station. Incase, the reverse power control sub-channel 543 indicates good receptionof the fundamental channel 481, the gain of the fundamental channel 481may be decreased to lower the Eb/Nt at the target mobile station.

The gain level of the supplemental channel 482 may be determined basedon the gain level selected for fundamental channel 481 in accordancewith an embodiment. Each data frame of supplemental channel 482 may beassociated with a fundamental channel 481 targeted for a specific mobilestation. Therefore, the gain level of supplemental channel 482 may bedetermined based on the selected gain level of an associated fundamentalchannel 481 in accordance with an embodiment. After the gain adjustmentsin the encoder and modulator blocks 861 and 862, the outputs passthrough a carrier modulation block 863. The resulting signal may beamplified before being transmitted from a set of antennas 864 to mobilestations 102-104.

The signals transmitted between mobile stations 102-104 and base station101 may propagate through a channel with various fading conditions. Anadditive white Gaussian noise (AWGN) channel condition approximates aslow fading channel condition for the signal. The forward link powercontrol loop used for controlling gain level of a channel between mobilestations 102-104 and base station 101 may use an Eb/Nt threshold levelsuch that the frame error rate is maintained at an adequate level. TheEb/Nt threshold may be maintained and selected by the forward link powercontrol loop such that the average channel gain is at a level above theAWGN channel level. The average channel gain may be maintained at alevel comparable to the AWGN level plus a margin. By allowing theaverage channel gain to be above the AWGN level, in a fading channelcondition, the frame error rate is maintained at an adequate level mostof the time. One frame out of many frames may arrive at a poor signal tonoise ratio causing a frame error at the receiver. Such a frame erroroccurs at the deep part of the channel fading condition.

Referring to FIG. 9, a graph 900 depicts an example of a channel fadingcondition 902 and the channel gain 901 with respect to time. The gain ofthe channel is at a peak level when the channel fading condition is at abottom point. The AWGN of the channel may be at a gain level 903. Theaverage gain of the channel with the power control may be set at anaverage gain level 904. The margin between gain level 903 and theaverage gain level 904 allows the communications over the channel to beat an adequate frame error rate under most fading conditions. Thecommunications at the bottom of the fade condition may result inerroneous reception of one or more frames. Such a channel gain model andthe associated power control scheme works very well for forwardfundamental channel 481 due to its continuous nature of communication toa mobile station over a period of time.

The communications over supplemental channel 482 targeted for the samemobile station may be sporadic. The supplemental channel 482 may beshared among several mobile stations 102-104. The channel condition offundamental channel 481 at each mobile station may not be the same. Thechannel condition at one mobile station may be better than others. Assuch, the communication on the supplemental channel may be based on apriority index for each frame of data. For example, if the priorityindex of a mobile station is higher than others and the mobile stationhas a forward supplemental channel 482 with base station 101, theimmediately following frame of data on the supplemental channel 482 maybe used to transmit data to the mobile station. The supplemental channelscheduler 860 may be used to schedule data at input 850 corresponding tothe mobile station with the highest priority index. In one example, thepriority index may be equal to the inverse of the product of the averagethroughput (T) and the channel gain of the associated forwardfundamental channel 481. A priority index may be calculated for eachmobile station.

The power level of forward fundamental channel 481 may be based on aperiodic feedback from the mobile station. The forward fundamentalchannel 481 normally has a continuous communications of data between thereceiver and the transmitter. Therefore, the average gain level 904 offorward fundamental channel 481 may be at a level above an absoluteminimum (AWGN) level that accounts for variations in the propagationchannel over time. The communications on forward supplemental channel482 may be sporadic for a mobile station depending on the priority indexof the mobile station. As such, the forward supplemental channel 482 andforward fundamental channel 481 do not experience similar channelconditions in accordance with an embodiment.

Referring to FIG. 10, a graph 1000 shows variation of a channel gain ofsupplemental channel 482 as determined in accordance with variousembodiments. The gain of the supplemental channel (Gsch) 482 may be setequal to the gain of the fundamental channel (Gfch) 481 plus an adaptivemargin (Ma). The gain of the supplemental channel (Gsch) 482 may alsodepend on a data rate factor in accordance with an embodiment. The datarate factor may be based on the data rate of supplemental channel 482(Rsch) and the data rate of the associated fundamental channel 481(Rfch). The adaptive margin Ma may change with every frame of datascheduled for the mobile station in accordance with an embodiment. Forexample, at an initial time, data frame 1, the Gsch may be at a level“A”. At the data frame 2, the next data frame scheduled for transmissionon supplemental channel 482 to the same mobile station, the Gsch isdropped by an amount to the level “B”. At the data frame 3, the nextdata frame scheduled for transmission on supplemental channel 482 to thesame mobile station, the Gsch is dropped again by an amount to the level“C”. At the data frame 8, the next data frame scheduled for transmissionon the supplemental channel 482 to the same mobile station, the Gsch isdropped again by an amount to the level “D”. The drop in thesupplemental channel gain Gsch may be accomplished by adjusting theadaptive margin Ma before each transmission.

If a data frame on the supplemental channel 482 is received in error,the Gsch for the next scheduled data frame is increased by an amountsufficiently large that, perhaps, provide adequate reception at thereceiver in accordance with an embodiment. In this case, at the dataframe 14, the next data frame scheduled for transmission on thesupplemental channel 482 to the same mobile station, the Gsch isincreased by an amount to the level “F”. The increase of thesupplemental channel gain Gsch from the gain level D to the gain level Fis sufficiently large that allows error-free communication. The increasein the supplemental channel gain Gsch may be accomplished by adjustingthe adaptive margin Ma before each transmission in accordance with anembodiment. If no frame error received after data frame 14, thesupplemental channel gain Gsch begins to drop successively by an amountafter each data frame scheduled for transmission on the supplementalchannel 482 to the same mobile station in accordance with an embodiment.

On the reverse power control sub-channel 543, in mode “110” of theforward power control modes, the even numbered power control groups areused to communicate power control bits relating to the fundamentalchannel 481, and the odd numbered power control groups are used tocommunicate data frame error via QIB or EIB associated with thesupplemental channel 482. The adaptive margin Ma is increased when aframe error is received, and decreased when a data frame is receivedwith error as indicated by QIB or EIB on the reverse power controlsub-channel 543 in accordance with an embodiment. In one example, if thegain of the forward fundamental channel Gfch and the data rate factorremain the same, the behavior of the adaptive margin Ma may be as shownin graph 1000. Therefore, the gain of the supplemental channel Gsch isdynamically controlled by determining the adaptive margin Ma before eachscheduled data frame transmission to the same mobile station inaccordance with an embodiment.

Referring to FIG. 11, a flow chart 1100 depicts a method for determiningthe adaptive margin Ma for a data frame transmitted on supplementalchannel 482 targeted for a mobile station in accordance with anembodiment. Various steps of flow chart 1100 may be performed by channelgain selector 890 in accordance with an embodiment. At a step 1101, theadaptive margin Ma may be initialized for the first data frame onsupplemental channel 482 targeted for the mobile station. Such aninitialization may be performed before transmitting the first data frameon supplemental channel 482 to the mobile station. At step 1102, onedata frame on supplemental channel 482 is transmitted to the mobilestation at a gain level Gsch based on at least the adaptive margin Ma.At step 1103, the channel gain selector 890 determines whether aprevious data frame transmitted on supplemental channel 482 to the samemobile station is received without error. Such information may becommunicated to the base station on the reverse power controlsub-channel 543. If the data frame is received without error, theadaptive margin Ma is decreased at step 1104 for a subsequent data frametransmitted to the same mobile station. If the data frame is receivedwith error, the adaptive margin Ma is increased at step 1105 for asubsequent data frame transmitted to the same mobile station. The amountof increase at step 1105 is much larger than the amount of decrease atstep 1104 in accordance with an embodiment. The increase at step 1105may be equal to 0.5 dB in comparison to a 0.005 dB decrease at step1104.

Those of skill in the art would further appreciate that the variousillustrative logical blocks, modules, circuits, and algorithm stepsdescribed in connection with the embodiments disclosed herein may beimplemented as electronic hardware, computer software, or combinationsof both. To clearly illustrate this interchangeability of hardware andsoftware, various illustrative components, blocks, modules, circuits,and steps have been described above generally in terms of theirfunctionality. Whether such functionality is implemented as hardware orsoftware depends upon the particular application and design constraintsimposed on the overall system. Skilled artisans may implement thedescribed functionality in varying ways for each particular application,but such implementation decisions should not be interpreted as causing adeparture from the scope of the present invention.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein may be implementedor performed with a general purpose processor, a digital signalprocessor (DSP), an application specific integrated circuit (ASIC), afield programmable gate array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with theembodiments disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination. A softwaremodule may reside in RAM memory, flash memory, ROM memory, EPROM memory,EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or anyother form of storage medium known in the art. An exemplary storagemedium is coupled to the processor such that the processor can readinformation from, and write information to, the storage medium. In thealternative, the storage medium may be integral to the processor. Theprocessor and the storage medium may reside in an ASIC. The ASIC mayreside in a user terminal. In the alternative, the processor and thestorage medium may reside as discrete components in a user terminal.

The previous description of the preferred embodiments is provided toenable any person skilled in the art to make or use the presentinvention. The various modifications to these embodiments will bereadily apparent to those skilled in the art, and the generic principlesdefined herein may be applied to other embodiments without the use ofthe inventive faculty. Thus, the present invention is not intended to belimited to the embodiments shown herein but is to be accorded the widestscope consistent with the principles and novel features disclosedherein.

1. In a communication system, a method for controlling gain of asupplemental channel comprising: determining gain level of a fundamentalchannel (Gfch), wherein said fundamental channel is associated with saidsupplemental channel for being targeted for a common receiving station;determining an adaptive margin (Ma) for said supplemental channel;adjusting said Ma based on errors and non-errors in the supplementalchannel before each scheduled data transmission to said common receivingstation; and determining a supplemental channel gain (Gsch) based onsaid Gfch and said Ma.
 2. The method as recited in claim 1 furthercomprising: transmitting said supplemental channel at said Gsch level.3. The method as recited in claim 1 further comprising: determining adata rate factor based on a data rate of said fundamental channel anddata rate of said supplemental channel, wherein said Gsch is based onsaid data rate factor.
 4. The method as recited in claim 1 furthercomprising: decreasing said Gsch for a subsequent data frame targetedfor said common receiving station by decreasing said Ma.
 5. The methodas recited in claim 1 further comprising: successively decreasing saidGsch for subsequent data frames targeted for said common receivingstation on said supplemental channel by successively decreasing said Ma.6. The method as recited in claim 1 further comprising: increasing saidGsch for a subsequent data frame targeted for said common receivingstation on said supplemental channel by increasing said Ma afterreceiving a supplemental channel frame erasure indicator from saidcommon receiving station.
 7. The method as recited in claim 1 furthercomprising: successively decreasing said Gsch for subsequent data framestargeted for said common receiving station on said supplemental channelby successively decreasing said Ma until receiving a supplementalchannel frame erasure indicator from said common receiving station. 8.The method as recited in claim 7 further comprising: increasing saidGsch for a subsequent data frame targeted for said common receivingstation on said supplemental channel by increasing said Ma afterreceiving said supplemental channel frame erasure indicator from saidcommon receiving station.
 9. In a communication system, an apparatus forcontrolling gain of a supplemental channel comprising: a channel gainselector for determining gain level of a fundamental channel (Gfch),wherein said fundamental channel is associated with said supplementalchannel for being targeted for a common receiving station, determiningan adaptive margin (Ma) for said supplemental channel and adjusting saidMa based on errors and non-errors in the supplemental channel beforeeach scheduled data transmission to the common receiving station anddetermining a supplemental channel gain (Gsch) based on said Gfch andsaid Ma.
 10. The apparatus as recited in claim 9 further comprising: atransmitter for transmitting said supplemental channel at said Gschlevel.
 11. The apparatus as recited in claim 9 wherein said channel gainselector determines a data rate factor based on a data rate of saidfundamental channel and data rate of said supplemental channel, whereinsaid Gsch is based on said data rate factor.
 12. The apparatus asrecited in claim 9 wherein said channel gain selector decreases saidGsch for a subsequent data frame targeted for said common receivingstation on said supplemental channel by decreasing said Ma.
 13. Theapparatus as recited in claim 9 wherein said channel gain selectorsuccessively decreases said Gsch for subsequent data frames targeted forsaid common receiving station on said supplemental channel bysuccessively decreasing said Ma.
 14. The apparatus as recited in claim 9wherein said channel gain selector increases said Gsch for a subsequentdata frame targeted for said common receiving station on saidsupplemental channel by increasing said Ma after receiving asupplemental channel frame erasure indicator from said common receivingstation.
 15. The apparatus as recited in claim 9 wherein said channelgain selector successively decreases said Gsch for subsequent dataframes targeted for said common receiving station on said supplementalchannel by successively decreasing said Ma until receiving asupplemental channel frame erasure indicator from said common receivingstation.
 16. The apparatus as recited in claim 15 wherein said channelgain selector increases said Gsch for a subsequent data frame targetedfor said common receiving station on said supplemental channel byincreasing said Ma after receiving said supplemental channel frameerasure indicator from said common receiving station.
 17. Acommunication system comprising: a transmitter for determining channelgain of a supplemental channel based on a fundamental channel gain of afundamental channel and for determining a channel adaptive gain marginfor said supplemental channel and adjusting said channel adaptive gainmargin based on errors and non-errors in the supplemental channel beforeeach scheduled data transmission to a common receiving station, whereinsaid fundamental channel and said supplemental channel are targeted forsaid common receiving station.
 18. The system as recited in claim 17wherein said transmitter transmits said supplemental channel to saidcommon receiving station at said determined channel gain.
 19. The systemas recited in claim 18 wherein said transmitter decreases successively,at each frame of data targeted for said common receiving station, saiddetermined supplemental channel gain by decreasing successively saidchannel adaptive gain margin and transmits, at said each frame of datatargeted for said common receiving station, said supplemental channel tosaid common receiving station at said successively reduced gain leveluntil a supplemental channel frame error indicator is received from saidcommon receiving station.
 20. The system as recited in claim 18, afterreceiving a supplemental channel frame error indicator from said commonreceiving station, wherein said transmitter increases at a next frame ofdata said determined supplemental channel gain by increasing saidchannel adaptive gain margin and transmits at said next frame of datasaid supplemental channel to said common receiving station at saidincreased gain level.
 21. The system as recited in claim 17 furthercomprising: a receiver in said common receiving station for receivingsaid supplemental channel and said fundamental channel; a controller insaid common receiving station for determining a supplemental channelframe error rate of said supplemental channel.
 22. An apparatus forcontrolling gain of a supplemental channel comprising: means fordetermining gain level of a fundamental channel (Gfch), wherein saidfundamental channel is associated with said supplemental channel forbeing targeted for a common receiving station; means for determining anadaptive margin (Ma) for said supplemental channel; means for adjustingsaid Ma based on errors and non-errors in the supplemental channelbefore each scheduled data transmission to said common receivingstation; and means for determining a supplemental channel gain (Gsch)based on said Gfch and said Ma.
 23. The apparatus as recited in claim 22further comprising: means for transmitting said supplemental channel atsaid Gsch level.
 24. The apparatus as recited in claim 22 furthercomprising: means for determining a data rate factor based on a datarate of said fundamental channel and data rate of said supplementalchannel, wherein said Gsch is based on said data rate factor.
 25. Theapparatus as recited in claim 22 further comprising: means fordecreasing said Gsch for a subsequent data frame targeted for saidcommon receiving station by decreasing said Ma.
 26. The apparatus asrecited in claim 22 further comprising: means for successivelydecreasing said Gsch for subsequent data frames targeted for said commonreceiving station on said supplemental channel by successivelydecreasing said Ma.
 27. The apparatus as recited in claim 22 furthercomprising: means for increasing said Gsch for a subsequent data frametargeted for said common receiving station on said supplemental channelby increasing said Ma after receiving a supplemental channel frameerasure indicator from said common receiving station.
 28. The apparatusas recited in claim 22 further comprising: means for successivelydecreasing said Gsch for subsequent data frames targeted for said commonreceiving station on said supplemental channel by successivelydecreasing said Ma until receiving a supplemental channel frame erasureindicator from said common receiving station.
 29. A processor-readablemedium including processor-executable instructions encoded thereon forperforming a method for controlling gain of a supplemental channelcomprising: determining gain level of a fundamental channel (Gfch),wherein said fundamental channel is associated with said supplementalchannel for being targeted for a common receiving station; determiningan adaptive margin (Ma) for said supplemental channel adjusting said Mabased on errors and non-errors in the supplemental channel before eachscheduled data transmission to said common receiving station; anddetermining a supplemental channel gain (Gsch) based on said Gfch andsaid Ma.
 30. The processor-readable medium as recited in claim 29further comprising processor-executable instructions for: transmittingsaid supplemental channel at said Gsch level.
 31. The processor-readablemedium as recited in claim 29 further comprising processor-executableinstructions for: successively decreasing said Gsch for subsequent dataframes targeted for said common receiving station on said supplementalchannel by successively decreasing said Ma.
 32. The processor-readablemedium as recited in claim 29 further comprising processor-executableinstructions for: increasing said Gsch for a subsequent data frametargeted for said common receiving station on said supplemental channelby increasing said Ma after receiving a supplemental channel frameerasure indicator from said common receiving station.